Hospitals in 23 rural Florida counties are threatening to stop delivering babies for poor women when a state fund dries up Oct. 1, but the problem of treating the indigent may become most severe in urban Orange County.

Orlando Regional Medical Center has told the county it plans to greatly reduce the number of welfare patients it treats, including children and men. Poor pregnant women will be most affected. The hospital, which now handles 1,200 welfare deliveries a year, wants to cut the number to 400.

''There's no way we could get that number of women delivered at other hospitals,'' said Dr. Betty Vaughn, assistant director of the Orange County Health Department.

Across the state, county health departments are hitting snags in annual contract negotiations with hospitals that care for the poor, said an official of the Florida Department of Health and Rehabilitative Services.

Hospitals in some rural counties are ''making threatening noises'' that they will stop delivering babies for women on welfare when the state's Improved Pregnancy Outcome Program stops reimbursing them for deliveries Oct. 1, said Sally Wendt of Tallahassee, who oversees the program.

None of the hospitals are in Central Florida.

Wendt said state lawmakers this year ordered that the program spend money only on prenatal care for poor women, not hospital deliveries. Last year, the program provided prenatal care to 41,800 women. To qualify, the patient from a family of four can earn no more than $14,400.

Unlike in urban counties, many rural hospitals receive no county funds for indigent births. To get these hospitals to participate in the prenatal program and deliver welfare babies, the state has been footing the bill.

State health officials now believe they can get ''the most for our money'' from prenatal care because it leads to fewer babies with birth defects who need the help of other state programs, Wendt said.

Last year the state spent $5.3 million for prenatal care and deliveries. This year the Legislature eliminated money for births but gave $7 million to provide better prenatal care for more women.

Wendt said lawmakers considered it unfair that the state reimbursed some hospitals and not others for delivering poor women's babies.

ORMC never received reimbursement from the state prenatal program for indigent deliveries, and its planned cutback was not prompted by the Legislature's action.

The hospital is reimbursed by county welfare funds and state Medicaid funds for most indigent births. However, neither government program pays ORMC what it would make from a private patient.

Vaughn said Orlando General Hospital has offered to deliver the babies of some of the welfare mothers ORMC turns away, but ''they have just a small obstetrics unit. They couldn't hope to pick up the slack.''

ORMC officials refused Tuesday to discuss details of their plan, saying they first want to present it to the Orange County Commission.

In a report sent to county officials last week, the hospital said it treats 69 percent of the county's indigent population. ORMC wants to reduce that to 34 percent. It believes other area hospitals should take ''their fair share.'' ''We feel it's inappropriate and a disproportionate burden on ORMC, and to our paying patients, the way the current structure is set up,'' said spokesman Joe Brown.

The hospital's cutback, planned for Oct. 1, also will affect children and adults who cannot afford a private doctor and receive care from the Health Department or the Orange County Medical Clinic. A family of four must earn less than $9,600 a year to qualify for the county's medical assistance program.

''If what they propose comes to fruition, a substantial number of patients would be affected,'' said Dan Kirshner, the manager of Orange County Social Services.

''I don't deny that Orlando Regional takes a disproportionate share of indigents in the county, but it's not something that happened yesterday and to have the expectation that it's going to be changed in 2 1/2 months, with the constraints in the medical delivery system we have, that's a little bit much,'' he said.

Kirshner said ''it could be unfortunate for some folks'' if the cutback takes effect ''without a rational plan'' for changing the delivery of health care services to the poor.

According to the hospital's report, ORMC lost at least $6.8 million by treating welfare patients during the fiscal year that ended Sept. 30.

''In the past we have made up these deficits by charging more to other patients,'' the report says. It can no longer afford to pass costs along to paying patients because of competitive pressures in the health care market.